-LRB- CNN -RRB- -- Marie Mills held her 77-year-old father , who had collapsed outside in a Washington street . She screamed for help .

A passerby rushed across the street to bang on the door of a fire station , knowing that firefighters are trained to provide emergency medical help .

But they would n't leave the station .

The same thing happened when two more people tried to summon the firefighters for assistance , Mills says .

`` We looked across the street at the fire station . There was a firefighter that was actually standing against the fire apparatus , '' she told CNN affiliate WJLA . `` Everybody started trying to wave him over . '' But the firefighter said he had to be dispatched first .

`` I even ran to the curb and said , ` Are you going to help me or let my dad die ? ' '' said Mills .

Later , after an ambulance finally arrived , Cecil Mills died at a hospital . He had suffered an apparent heart attack .

An investigation is under way and , so far , no officials are publicly challenging Mills ' version of events .

`` It 's an outrage , '' Washington Mayor Vincent Gray said at a news conference . `` I was absolutely furious . ''

He said he apologized to Marie Mills for `` what appeared to be dereliction , '' DC news station WTTG reported .

`` Those who failed to respond as they should -- they will be held accountable , period , '' Gray vowed .

In comments Thursday to CNN , Gray said he has `` taken a lot of time with it . ''

The investigation is `` being done as rapidly as we possibly can , '' he added .

The D.C. Fire and Emergency Medical Services Department told CNN it is investigating the incident , which took place along the 1300 block of Rhode Island Avenue on Saturday .

`` Our duty is to respond to all requests for emergency assistance . If it is determined that proper protocols were not followed at the conclusion of our investigation , then appropriate action will be taken , '' spokesman Tim Wilson said .

The protocol is in question because , according to the Mills family , those who asked for help at the fire station were told to call 911 .

Calls to 911 were placed , but a mix-up with the address delayed an ambulance , said Washington Council member Tommy Wells .

`` Two things happened , '' he said . `` One was that no one came out of the fire house to help this gentleman . The other is the ambulance that was dispatched was dispatched to the wrong place . This was a number of fiascos . ''

Paul Quander , deputy mayor for public safety , said a `` very new , probationary employee '' was at the facility . The employee 's first response should be `` to ask a senior person , and we believe that was done , '' he said , according to WTTG . `` The question now is what did that senior person say ? What did that person do ? Did they follow protocols and procedures ? ''

There are no protocols that would prevent fire personnel from helping those in need , Quander told CNN Thursday . `` These are people who run into burning buildings . They work in the most hazardous conditions imaginable .

`` They cross the streets , they cross highways to get to people . It is understood . It is common . This is why it is so troubling that we did not take the appropriate action in this case . It 's right across the street . ''

`` It 's hard to get your arms around '' the idea that this took place , he added .

Lt. Kellene Davis was the officer in charge of the station at the time of the incident , WTTG reports .

Davis did not respond immediately to an e-mail Thursday from CNN , and a call to a phone number listed for her was not answered .

Also Thursday , a spokesman said that two employees of the D.C. Fire and Emergency Medical Services Department have been suspended with pay in the wake of the incident .

`` I can not say who they were because it is a personnel matter and an ongoing investigation , but I can tell you that neither of them was the probationary firefighter involved in the incident , '' said Keith St. Clair , with the office of the deputy mayor for public safety .

The employees were working at the station , he said .

Cecil Mills , a lifelong Washington resident , worked for the Department of Parks and Recreation .

His daughter , in mourning , had kind words for the mayor 's handling of the matter . `` I appreciate how seriously he is taking this because it never should have happened , '' she told WTTG .

Marie Mills was n't immediately available Thursday when contacted by CNN .

The firefighters ' union said the incident simply should never have happened .

`` We need to find out why it did occur and make sure it never happens again , '' said Ed Smith , president of the DC Fire Fighters Association , in a statement reported by WTTG .

He added that on the union 's behalf , `` I offer Mr. Mills ' family a sincere apology . ''

CNN 's Aaron Cooper and Mike M. Ahlers contributed to this report from Washington .

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NEW : Two employees have been suspended with pay , a spokesman says

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Three people tried to summon firefighters to help the collapsed man

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Mills ' daughter said she saw a firefighter at the station

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That firefighter , a new employee , apparently said he had to be dispatched to help